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M42 does not idle right or at all diag tree .


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READ THROUGH THIS FIRST BEFORE BUYING SOMETHING THIS IDLE IS TRICKY TO DIAG.

 

(if you  have any techincal questions about this issue please look through my previous posts i have uploaded all the service manuals for the m42 i can find , before you dm me ) 

I made this really easy just click the tag m42swap all one word  not two different/ separate words.

 

BEFORE YOU BUY ANYTHING OHM OUT ALL THE SENSORS ESPICALLY THE CAM AND CRANKSHAFT SENSOR (im updating this as i find ,startup issues ) please see my sensor diag post for the specifics . click the m42swap tag and you should be able to find it . 

 

first test and or replace the IAC (Idle air control valve )   this is 80% chance the answer  you can order one off amazon

 

( https://www.amazon.com/Aluminum-13411433627-Replacement-

13411247197-13411709932/dp/B08CZV8W3R/ref=sr_1_1?dib=eyJ2IjoiMSJ9.nrMILMbdsLPRq4JWYnkxRFPHya-bv_kflUBlrduIYriE7dhEcyOXHrnsO2wfuxk8f5Mowp3sqdB38QEyAvz3WvEyIOcAzgn6xHqG8des83uwElq43OX7I5YKDueJc-nOgi6YimQhEjKqvkCqMqaLaHQXXbjVyg9bT4XIAB-QCdNzypY6ctVJ1MQS7hyQt1TO8YIlqtA1QMlZgMPhhPWtfsP_I_4mz8TAEo8Y502rn3c.tNi2tj2fmbitxtcmTd74f7hMwtXZinon2I-kUKvbXPg&dib_tag=se&keywords=13411433627&qid=1710024790&sr=8-1)

 

( a hint for the newbies to this engine the IAC is directional ,   and if your car idles at 3000rpm on a cold idle it is a 100% this one i know from experience )   part number for the iac is      :        (  13411433627   )

 

second test  for idle test the intake  for leaks leaks using a smoke machine from directly behind the AFM (aka remove the afm then smoke test it )

 

third  test the throttle sensor  60 % chance that this is the issue  ( part number for replacement 13637840383 ) 

 

4th test and place the water temp sensor ( if your m42 does want to cold start or  revs way up and DIES  i would do this second  most likely to be your problem )the  blue one 

that is closer to the oil filter housing  and connected by the brown connector

(part number 13621709967)  ( hint if this ohms out ok , ohm out the camshaft sensor it will most likely be your culprit #7 (in the list)) 

 

 

 (  HINT for m42 into 2002 you have to replace  the sensor that closer to the firewall with this one ( part number 62-11-1-268-355   )  BMW /OE ONLY FOR THIS AS WELL

this sensor is for the temp gauge THIS IS NOT THE BLUE SENSOR THE BLUE SENSOR THAT  HAS TWO PINS THIS  IS  ONE HAS ONE PIN )  for  the  stock dash temp gauge to work right).

Link to the part 

WWW.PELICANPARTS.COM

Genuine BMW Temperature Sending Unit Temperature Gauge InStock Ships Today! $37.50. Call (310)626-8765. May Qualify For FREE SHIPPING. Parts# 62 11 1 268 355 62-11-1-268-355 62.11.1.268.355 62111268355. Bavaria, 533i, 530i, 528i, 528e, 325e, 320i, 3.0CS, 2800CS, 2002tii, 2002, 1602, 1600.

 

 

5th i would replace  the 02 sensor . ( use oem /oe parts on this , bosh is the best for this ). ( part number 11781734796 ) ( link to part 

WWW.BIMMERWORLD.COM

Direct Fit OEM Oxygen Sensor

 

 

 

6th the  AFM  ( AIR FLOW METER ) its really expensive to get done right and the amazon ones are not worth your time.

 

here is the link to the guy who redoes them properly .  (  

BAVREST.COM

Bavarian Restoration refurbishes all Bosch Air Flow Meters to meet factory specifications. Let me tell you that this is one of the most important sensors for your engine. After 10 or so years, these...

If you insist on buying a new one here is the part number  (       13627558785KT  )

(ps a brand new one is $972 a rebuild is much cheaper ).

 

 

7th the crankshaft sensor , if the motor does nothing doesn't crank / doesn't start 95.99999999% it is this sensor or a dead battery  ( part number for the sensor is  12-14-1-721-504)

 

******* the only compatible sensor for this is the BMWs genuine part , if you order  the crankshaft sensor  and it looks like this with the bolt tab in line with the wire

this sensor is mislabeled as compatible with the e30 m42 , the e36 m42 i don't know but i wouldn't bet on it .   The good sensor has the bolt  tab clocked at (25 degrees roughly)

from the wire this is the correct one . please see good pictures after bad ones .  

 

 

The  first pictures listed below  are the pictures of the bad sensor .

 

IMG_9092.thumb.jpg.16644def0ef5c27fd244bd735ab6a343.jpgIMG_9091.thumb.jpg.8f9a9513fed35a81c7560c620e61b2f2.jpgIMG_9090.thumb.jpg.16ef8376aedd4fa2daeec39dc62fbd5f.jpgIMG_9089.jpg.a285f5af71019c358b9916a673fa777a.jpg

 

Pictures of the good style sensor are listed below 

 

correctcrankshaftsensorpic5.jpg.617c7ea2e8ead0919dc8937dd2492410.jpgcorrectcrankshaftsensorpic4.jpg.8bae22d0b9e4662acf26cb9afbf1a23b.jpgcorrectcrankshaftsensorpic3.jpg.b8c7e4f01d1d7364c90fe38d8d9f1ceb.jpgcorrectcrankshaftsensorpic2.jpg.47c68fb014d074a91e9c7b4814709606.jpgcorrectcrankshaftsensorpic1.jpg.0d7033d4e9cfeca1d78262bf62b899b8.jpg

ALL Credit to Turner motorsports for the good sensor pictures .

A link to this sensor on Turner motorsports . 

 

 https:// www.turnermotorsport.com/p-7114-crankshaft-position-sensor-e30-318is-w-m42-engine/

 

 A link to the cheapest  way to get the  BMW Genuine part .

PARTS.BMWNORTHWEST.COM

Genuine BMW Part # 12141721504 (12-14-1-721-504, 12141721968) - Pulse generator. Manual, Engine, Housing, Timing. Fits 318i, 318is. Ships from BMW Northwest, Tacoma WA

 

 

 

8th the camshaft sensor if the motor starts and then dies ( when only hot or cold ) , and you have  tested and ohmed out the coolant temp sensor 

this is your problem   (part number  is : 12-14-1-734-815)

 

9TH replace your dme or the engines computer i dont have a part number for you 

 

If NONE OF THESE OHM OUT BAD THE ONLY OTHER FIX I HAVE FOUND FOR THIS IS THAT YOUR  VALVE LIFTERS ARE WORN OUT  AND YOU MUST PUT A VERY THIN OIL 

0W-40 FOR EX . USE THIS AS A LAST RESORT ONLY AFTER YOU HAVE REPLACED THE  DME OR THE COMPUTER ( they are the same thing ) FOR THE ENGINE. 

 

 

if you 02 idle issue please dm me i am more than happy to help . 

 

 

 

 

 

 

 

Diag procedues for these sensors .

 

 

All credit goes to Desktop Dave  from the m42 club 

 

link to original post   (   http://www.m42club.com/forum/index.php?topic=17926.0 )

 

 

"

 

Airflow sensor (AFM) harness must have 5VDC between harness pin 1 and ground with ignition switched on. Pins 1&2 on the AFM will have a steady & variable resistance (ohms) as the door is moved through its travel. While you're there, test the intake air temp sensor (IAT). Pins 4&5 on the AFM should have 7-12Kohms resistance at 14degF, 2-3Kohms at 70degF. resistance will drop as the air temp gets higher.

 

 

 

Throttle position sensor is easy on the E30. With the ignition on, you'll need to have 5VDC between on pin 1 in the harness and ground. If the throttle is closed (idle position) you should see zero resistance (continuity) on sensor pins 1&2 and infinite resistance on pins 2&3. As you open the throttle plate, pins 1&2 must switch to infinite resistance. Move your DMM leads to pins 2&3. They must have infinite resistance until the throttle is almost fully open (WOT), at which point you'll see zero resistance. Be sure to test the TPS while it is installed on the TB - switch mis-adjustment, throttle cable too tight or a sticking throttle plate can prevent it from working properly. There are two slotted leads that permit limited adjustment of the TPS. I usually clean the TB with some alcohol/TB cleaner and a few shop cloths while I'm testing it out.
An E36 sensor is similar, but with a variable resistance. It'll also have 5VDC on harness pin 1. TPS pins 1&2 should increase resistance from 1-4Kohm as the throttle opens, pins 1&3 should read out approx. 4Kohms. Be aware that there is also a secondary TPS on E36 models with traction control...I'm not sure if the M42 models had this option or not.

 

 


The O2 sensor isn't easy to test properly. You can attempt to troubleshoot it with the following tests. The O2 sensor will output a rapidly fluctuating 0.2-0.8VDC signal when fully heated (>300degF) on pins 1&2 (be aware of dangerously hot components if attempting this test). Pins 3&4 on sensor harness (heater circuit) must have continuity. There must be battery voltage on pins 3&4 in the engine harness when the ignition switch is in position II. "

 

IAC diag i will provide a YouTube link . 

 

All credit goes to Nathans BMW Workshop on YouTube 

 

image.png

Edited by M4202
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